In this study, we analyzed polychlorinated biphenyls (PCBs) in the blood of Yusho patients collected from medical check-ups, which were conducted in 2012. The results show that 65 PCB isomers, not including non-ortho PCBs, were detected in the blood samples, and the total concentration was 620 ng g^<-1> lipid. This value was comparable to the concentration in blood samples collected in 2005, and indicated that PCB concentrations in Yusho patients remained unchanged from 2005 to 2012. Here, we focused onmajor and specific PCB isomers in the blood samples of Yusho patients and normal controls. Examples of the former include hexaCB-153, hexaCB-138, and heptaCB-180, which are detected in human blood, while the latter include hexaCB-156, hexaCB-157, and heptaCB-189, and are highly detected in the blood of Yusho patients. Additionally, we tried to determine why the specific isomers were highly accumulated in the blood of Yusho patients as compared to the normal controls. We therefore analyzed these isomers in the contaminated rice oil, and found that the concentrations of hexaCB-156, hexaCB-157, and heptaCB-189 were 1800, 450, and 190 ng g^<-1>, respectively. Notably, previous studies indicated that these isomers m ight not be easily metabolized in humans. Therefore, these findings demonstrated that these isomers were highly accumulated in the blood of Yusho patients.2012 年に実施したカネミ油症検診において，油症患者から血液を採取して，PCB 分析を実施した．その結果，患者における総PCB 濃度の平均値は620 ng g^<-1>（脂肪重量換算）であり，2005年の濃度結果とほぼ同等であった．本研究では，ヒト血液中から高濃度で検出される主要異性体（hexaCB-153，hexaCB-138 及びheptaCB-180）と油症患者の血液から高濃度で検出される特定異性体（hexaCB-156，hexaCB-157 及びheptaCB-189）に注目し，なぜ油症患者に特定異性体が残留しているのか，その原因について調査した．その結果，油症の原因となったライスオイルから，hexaCB-156，hexaCB-157 及びheptaCB-189 が，それぞれ1800，450，190 ng g^<-1>で検出され，これらの異性体が極めて高い濃度で含まれていることが明らかになった．また，PCBs 代謝に関する過去の研究報告から，特定異性体は主要異性体とは異なり，代謝されにくい構造を持つ物質であることが示唆された．以上のことから，油症発症から40 年以上が経過した現在でも，特定異性体は油症患者の体内において高いレベルで残留していると考えられた．